The objective of this project is to design, fabricate, and test co-located earphones/microphones for use in in- ear, active noise reduction (ANR) systems. Our innovation is based on a micromachined membrane that serves as both the sensing element for a microphone and simultaneously the actuation surface for the earphone. By collocating the earphone and microphone, our device eliminates the acoustic phase delay between the ANR sensor and actuator, thereby enabling feedback algorithms with higher gain at higher frequency than is possible using separate devices. Current hearing protection designs provide approximately 30 dB of attenuation at the ear. This level of protection is not sufficient to allow long exposures in many industrial noise environments (which may exceed 130 dB) while maintaining the at-the-ear sound levels within prescribed safety limits. In order to keep within current NIOSH and OSHA noise exposure standards, new technologies are needed that will protect individuals from long-term exposure to harmful noise levels that could potentially result in temporary or permanent hearing threshold shifts. During the Phase I project, we demonstrated the feasibility of our innovation by fabricating and testing prototypical devices. The results we achieved showed the sensitivity of our microphone design, demonstrated the sound production capability of our earphone design, provided a manufacturing plan for fabrication of the co-located earphone/microphone during Phase II, and demonstrated the noise reduction capability over the frequency range of 300 Hz 8000 Hz. PUBLIC HEALTH RELEVANCE Noise-induced hearing loss ranks as one of the top 10 work-related issues by the National Institute for Occupational Safety and Health affecting individuals in the U.S. The goal of this project is to develop new technology for in-ear communications and hearing protection devices that will have greater hearing protection capability over a wider frequency range than is currently possible. [unreadable] [unreadable] [unreadable] [unreadable]